Apple's Next Big Leap Forward

Apple is yet to tap the world's biggest pool of potential iPhone buyers: China Mobile's customers. That is set to change. When and how will help determine whether the U.S. technology company's flagging stock can regain momentum.

At about $395, Apple's shares have fallen 44% from an all-time high hit last September. Once the most valuable company in the world by market capitalization, it recently ceded that crown back to Exxon Mobil....